(1) Field of the Invention
The present invention relates to a solid-state image sensor used for a digital camera and the like, and particularly to light-receiving cells which constitute the solid-state image sensor.
(2) Description of the Related Art
A general solid-state image sensor includes plural light-receiving cells formed on a semiconductor substrate, each of which has a photoelectric conversion unit which converts incident light entering through an aperture in a light-blocking film into signal charge and a color filter which is formed on the light-blocking film and separates the incident light based on colors. A primary color filter or a complementary color filter is commonly used as a color filter. Red (R), blue (B) and green (G) are used for primary color filters, and cyan (C), magenta (M) and yellow (Y) that are complementary colors of red, green and blue are respectively used for complementary color filters. In general, the solid-state image sensor using complementary color filters uses signals obtained through those three complementary color filters and the green (G) filter. One of the color filters is assigned, in a predetermined pattern, to each light-receiving cell. Accordingly, each light-receiving cell generates a signal in accordance with a luminance of a color signal obtained by color-separation through a respective color filter (e.g. refer to Japanese Laid-Open Patent Application No. 10-341012 and Japanese Laid-Open Patent Application No. 5-326902).
Furthermore, a S/N ratio is increased by forming microlenses and the like above and below color filters in order to increase the signals to be generated and realize high sensitivity (e.g. refer to Japanese Laid-Open Patent Application No. 2000-164837).
As a means of realizing high sensitivity in a solid-state image sensor, there is a suggested method of condensing light using total reflection at boundaries between high refractive index materials and low refractive index materials by positioning, in apertures of a light-blocking film, the high refractive index materials and the low refractive index materials so that the low refractive index materials surround the high refractive index materials (e.g. refer to Japanese Laid-Open Patent Application No. 6-224398).
FIG. 1 is a diagram showing a structure of a camera using a solid-state image sensor.
In this camera, incident light 24 reaches a solid-state image sensor 3 in a camera 2 through a camera lens 34.
FIG. 2 is a diagram showing an arrangement of light-receiving cells in a conventional solid-state image sensor.
In this solid-state image sensor, an image is obtained by which light-receiving cells (light-receiving cells positioned in a center A and peripheries B, C and the like) arranged in rows and columns convert, into signal charge, light entering through the camera lens 34 shown in FIG. 1.
FIG. 3 shows a cross-section diagram of light-receiving cells 1a, 1b and c of the conventional solid-state image sensor.
Each light-receiving cell is made up of an insulating layer 13, a metal layer 14 and a color filter layer 15 that are formed on a semiconductor substrate 11 made of silicon doped with N-type impurities. Here, a photoelectric conversion layer 12 is formed in the semiconductor substrate 11. The photoelectric conversion layer 12 includes P-type wells 16 formed by implanting P-type ion impurities in the semiconductor substrate 11 and photoelectric conversion units 17 that are N-type regions formed by further implanting N-type ion impurities in the respective P-type wells 16.
The insulating layer 13 is made up of an interlayer film 18 positioned on the photoelectric conversion layer 12 so as to insulate between the photoelectric conversion layer 12 and the metal layer 14.
The metal layer 14 includes a light-blocking film 19 and intralayer lenses 30. In the formation of the metal layer 14, the light-blocking film 19 is formed and the interlayer film 29 is then formed as a planarizing layer on the light-blocking film 19. Further, the intralayer lenses 30 are formed after the interlayer film 29 is formed on the light-blocking film 19. On the intralayer lenses 30, the interlayer film 31 is formed so as to cover the surfaces of the intralayer lenses 30.
The color filter layer 15 includes a color filter made up of a is blue filter film 21a, a green filter film 21b and a red filter film 21c, and an interlayer film 22 formed on the color filter.
The incident light 24 entering from above the light-receiving cells 1a, 1b and 1c, is condensed by the microlenses 23 formed on the color filter, and passes through one of the blue filter film 21a, the green filter film 21b and the red filter film 21c. The light which has passed through the color filter is condensed again by the intralayer lenses 30 and passes through the apertures 20 and reaches the photoelectric conversion units 17. In the case where the light-receiving cells 1a, 1b and 1c are the large light-receiving cells, each having a square of 5.6 μm as in the case of the conventional solid-state image sensor, the width of each aperture 20 is 2.0 μm or greater. Accordingly, for example, visible light having a red wavelength that is a long wavelength of 650 nm and the like can pass through the apertures without being affected by the aperture widths. Furthermore, near-infrared light of a longer wavelength used for a dark-field camera and the like can also pass sufficiently through the apertures.